Hst drive circuit

ABSTRACT

The present invention makes it possible, in an HST drive circuit wherein an HST pump and an HST motor have been separately stored in a pump case and a motor case, to efficiently cool the HST drive circuit. A cooling line for, while discharging a relief oil from a charge circuit  9  for replenishing an HST closed circuit  5  with a pressure oil into a pump case  3 , making the discharged oil flow into a reservoir  7  through the pump case  3 , a communicating pipe  14 , a motor case  4 , and an oil cooler  16  is formed, so that hydraulic oil circulating through an HST pump  1 , an HST motor  2 , and the HST closed circuit  5  is cooled by an oil flowing through the cooling line.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the technical field of an HST drivecircuit provided in a construction machine such as a wheel loader and anagricultural machine such as a tractor.

BACKGROUND OF THE INVENTION

Generally, in a construction machine such as a wheel loader and anagricultural machine such as a tractor, an HST drive circuit can be usedas a power transmission mechanism to a travel device, and therein, insome cases, a hydraulic pump (HST pump) and a hydraulic motor (HSTmotor) are stored in one case, and in some cases, these are separatelystored in a pump case and a motor case.

Meanwhile, in the HST drive circuit, because hydraulic fluid circulatesin the closed circuit between the HST pump and HST motor, it isdesirable to provide a cooling function to suppress a rise intemperature of the circulating hydraulic fluid. Therefore, aconventional structure that an oil cooler is arranged at an upstreamside of a charge circuit (replenishing circuit) for replenishing an HSTclosed circuit with fluid (see Japanese Published Unexamined PatentApplication No. H6-3720, for example) has been known.

However, in the HST drive circuit, normally, pressure fluid of thecharge circuit is to be introduced into variable displacement units ofthe HST pump and HST motor so as to operate the variable displacementunits. Accordingly, as in the above-described patent document, if an oilcooler is arranged at an upstream side of the charge circuit, in, forexample, a case such as starting in winter, there is a concern that thefluid temperature of the charge circuit is excessively lowered toheighten oil viscosity, thus starting the variable displacement unitsbecomes difficult. Furthermore, as described above, in an HST drivecircuit wherein the HST pump and HST motor have been separately storedin a pump case and a motor case, it is necessary to sufficiently coolboth, therein exists a problem to be solved by the present invention.

DISCLOSURE OF INVENTION

In view of the circumstances as described above, the present inventionhas been created for the purpose of solving these problems, and aninvention according to claim 1 is, in an HST drive circuit formed byconnecting a hydraulic pump stored in a pump case and a hydraulic motorstored in a motor case in a closed circuit form, characterized in that acooling line for, while discharging a relief oil from a charge circuitfor replenishing the closed circuit with a pressure oil into the pumpcase, making the discharged oil flow into an oil tank, from the pumpcase, through the motor case, to an oil cooler is formed.

By providing the invention according to claim 1, it becomes possible toefficiently cool the HST drive circuit by the oil flowing through thecooling line leading to the reservoir through the pump case, motor case,and oil cooler, from the charge circuit, a rise in temperature of thehydraulic fluid circulating through the closed circuit can be securelysuppressed. In particular, by guiding the total quantity of oildischarged from the pump case to the motor case, an excessive rise intemperature inside the motor case can be effectively suppressed.Moreover, as in the art wherein an oil cooler has been arranged at anupstream side of a charge circuit, the concern that starting thecapacity variable units of the HST pump and HST motor becomes difficultcan also be avoided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an HST drive circuit diagram.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of the present invention will be described based onthe drawing. In FIG. 1, a travelling HST drive circuit provided in awheel loader is shown, and in this FIG. 1, 1 denotes a hydraulic pump ofa variable displacement type (hereinafter, referred to as an HST pump 1)rotated by a drive of an engine E, 2 denotes a hydraulic motor of avariable displacement type (hereinafter, referred to as an HST motor 2)for causing an output shaft 2 a interlocked and coupled with a traveldevice of the wheel loader to rotate, and the HST pump 1 and HST motor 2are separately stored in a pump case 3 and a motor case 4, respectively,and are connected via an HST closed circuit 5, so that hydraulic fluidcirculates between the HST pump 1 and HST motor 2.

In addition, 6 denotes a charge pump rotated by an engine drive, andthis charge pump 6 supplies oil suctioned from a reservoir 7, through afilter 8, to a charge circuit 9 formed inside a pump case 3. The chargecircuit 9 is connected to an HST closed circuit 5 via a check valve 10,and replenishes the HST closed circuit 5 with oil by a leaked amount. Acircuit pressure of this charge circuit 9 is determined by a chargerelief valve 11 incorporated in the pump case 3 and a relief oil fromthis charge relief valve 11 is to be discharged into the pump case 3.Furthermore, pressure oil of the charge circuit 9 is to be introducedthrough control pilot circuits 12, 13 into variable displacement units 1c, 2 c of the HST pump 1 and HST motor 2 so as to operate these variabledisplacement units 1 c, 2 c.

On the other hand, the pump case 3 and motor case 4 are connected sothat the case interiors are communicated with each other via acommunicating pipe 14. Furthermore, 15 denotes a discharging oil channelleading to the reservoir 7 from the motor case 4, and an oil cooler 16is arranged in this discharging oil channel 15.

And, as described above, a relief oil from the charge relief valve 11 isdischarged into the pump case 3, wherein the discharged oil lubricatesand cools the inside of the pump case 3 and furthermore flows into themotor case 4 via the communicating pipe 14 to lubricate and cool theinside of the motor case 4. Thereafter, the discharged oil passesthrough the discharging oil channel 15 and returns to the reservoir 7after being cooled by the oil cooler 16, thus a cooling line in a serialform flowing into the reservoir 7 from the charge pump 6, through thepump case 3 and motor case 4, to the oil cooler 16 is formed.

Here, in FIG. 1, 17 denotes a main pump rotated by an engine drive, andthis main pump 17 is structured so as to become a hydraulic pressuresupplying source of a steering drive unit and an operating machine driveunit of the wheel loader (neither of these is shown).

Furthermore, 18 denotes a bypass line leading to the reservoir 7 fromthe pump case 3, and in this bypass line 18, arranged is a bypass valve19 which opens when pressure of the bypass line 18 becomes a preset setpressure or more. And, when oil viscosity is heightened during a time oflow temperature such as in winter, the bypass valve 19 opens to let theoil flow into the reservoir 7 from the upstream side of the coolingline, whereby it becomes possible to effectively prevent the pressure ofthe whole cooling line from becoming excessively great. In addition,when the bypass valve 19 opens, the oil flowed out of the pump case 3and motor case 4 is to flow into the reservoir 7 without passing throughthe oil cooler 16, therein an effect exists such that, during a time oflow temperature such as in winter, oil temperature can be efficientlyraised to a temperature suitable for operating hydraulic equipment.

In the present embodiment structured as has been described, in the HSTdrive circuit, a cooling line for making a relief oil discharged intothe pump case 3 via the charge relief valve 11 from the charge pump 6flow into the oil tank 7 through the communicating pipe, motor case 4,and oil cooler 16 has been formed, and by an oil flowing through thiscooling line, hydraulic oil circulating through the HST pump 1, HSTmotor 2, and HST closed circuit 5 is cooled.

As a result, even when the HST pump 1 and HST motor 2 are stored in theseparate pump case 3 and motor case 4, respectively, the hydraulic oilcirculating through the HST pump 1, HST motor 2, and HST closed circuit5 can be efficiently cooled by the oil flowing through the cooling line,therefore, even if the HST drive circuit is continuously driven for along time, a rise in temperature of the hydraulic fluid can be securelysuppressed. In particular, because the total quantity of oil which flowsout of the pump case 3 is to be guided to the motor case 4, this iseffective for suppressing a rise in temperature inside the motor case 4.Moreover, as in the prior art wherein an oil cooler has been arranged atan upstream side of a charge circuit, the concern that starting thevariable displacement units 1 c, 2 c of the HST pump 1 and HST motor 2becomes difficult can also be avoided.

Here, as a matter of course, the present invention can be employed notonly in HST drive circuits for travelling wheel loaders but also invarious HST drive circuits for construction machines other than wheelloaders and agriculture machines such as tractors, etc.

INDUSTRIAL APPLICABILITY

As in the above, an HST drive circuit according to the present inventionis useful as various HST drive circuits for construction machines suchas wheel loaders and agriculture machines such as tractors, etc., and issuitable, in particular, for such a case where the HST drive circuit iscontinuously driven for a long time.

1. An HST drive circuit formed by connecting a hydraulic pump stored ina pump case and a hydraulic motor stored in a motor case in a closedcircuit form, wherein formed is a cooling line for, while discharging arelief oil from a charge circuit for replenishing the closed circuitwith a pressure oil into the pump case, making the discharged oil flowinto a reservoir, from the pump case through the motor case to an oilcooler.